Some effort is being expended during the specification phase of contemporary broadband wireless communication standards such as the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) protocol, also referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access or E-UTRA, to improve the performance and efficiency of the power amplifier (PA) in mobile terminals or user equipment (UE). Toward this objective, there are a number of key performance metrics, but the over-riding goal is to minimize the PA power consumption (or peak and/or mean current drain), cost and the complexity required to deliver a given specified conducted power level, for example, +21 dBm or +24 dBm, to the UE antenna.
Generally, the required conducted power level must be achieved within a specified lower bound on in-band signal quality, or error vector magnitude (EVM) of the desired waveform, and an upper bound of signal power leakage out of the desired signal bandwidth and into the receive signal band of adjacent or alternate carrier receivers. These effects may be subsumed into the broader term “waveform quality”.
These problems represent classical PA design challenges, but emerging broadband wireless networks such as 3GPP LTE must solve these problems in the context of new modes of system operation. For example, PA operation must be optimized while transmitting new waveform types, including multi-tone waveforms and frequency-agile waveforms occupying variable signal bandwidths (within a nominal bandwidth, sometimes referred to as a channel or carrier bandwidth). Further, PA performance must now be optimized in a predominantly packet switched (PS) network where a network entity, such as a base station, schedules multiple wireless communication entities or terminals to transmit simultaneously. PA performance also must be optimized in the presence of numerous different frequency or spatially adjacent radio technologies, including GSM, UMTS, WCDMA, and unlicensed transmitter and receivers, among other radio technologies.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.